Adhesive composition laminate with butyl rubber

ABSTRACT

A roofing adhesive particularly suited for use in connection with membrane roofing materials such as EPDM or neoprene is preferably compounded from butyl rubber, a cross-linking system for the butyl rubber and a tackifier. The tensile strength, elongation, modulus at 300% elongation and modulus at failure of the composition are adjusted within range by choice of components and concentration. The adhesive composition may preferably be formed into a tape for joining sheets of the membrane roofing material.

This is a continuation of copending application Ser. No. 008,775, filedJan. 30, 1987, now abandoned, which is a division of abandonedapplication Ser. No. 771,250, filed Aug. 30, 1985, which is acontinuation of abandoned application Ser. No. 482,220, filed Apr. 5,1983.

FIELD OF THE INVENTION

The present invention relates to the field of adhesive compositions andmore particularly to the field of adhesive compositions for use inconnection with membrane roofing materials such as EPDM (ethylenepropylene diene monomer) and neoprene. The adhesive composition may beprepared in a single layer to form a one ply tape or may be applied to astrip of membrane roofing material to form a cover strip.

BACKGROUND OF THE INVENTION

In the field of roofing, increasing use is being made of membraneroofing materials such as EPDM (ethylene propylene diene monomer) andneoprene. Sheets of such materials are generally prepared by a doublecalendering process in which two sheets of uncured material are pressedtogether by rollers to form a single sheet. The composite single sheetis then generally coated with talc, wound into a roll and cured.

Although this calendering process virtually eliminates leakage problemsarising from small defects such as pinholes in either of the twooriginal sheets, it increases the cost of the finished product.

The membrane roofing materials are available in sheets of standardwidths. Successive sheets of the membrane roofing material are splicedtogether to form a continuous sheet which covers the roof. Lap jointsare typically used to splice adjacent sheets of roofing material. Toform such a joint, sheets of the material are positioned adjacent to oneanother such that they overlap about three inches along the edges to bejoined. The edge of the overlying sheet is then folded back such thatthe contact surfaces of the edges are exposed. The term "overlap" asused herein and in the claims below includes sheets that are overlappedbut folded back as well as sheets which are overlapped and not foldedback. The overlapping surfaces are then cleaned with a solvent such ashexane, toluene or white gasoline to remove talc or other foreignmaterial which might impair the strength of the bond. A contact adhesiveis then applied to the contact surfaces and allowed to dry. The sheetsare then repositioned in overlapping relation and the overlapping areasare pressed together by a roller which is rolled along the joint.

The strength of the lap joint may be improved by use of a primer. Suchprimer is best applied to the overlapping surfaces of the membraneroofing material after cleaning with solvent but before application ofthe contact adhesive. The primer may also be used by scrubbing orbrushing it onto the overlapping surfaces without cleaning.

This method of joining sheets of roofing material is extremely slow andlabor intensive. In addition, the lap joint formed by this method mustbe sealed with a caulking compound to prevent penetration of moisturealong the seam.

An alternate method of joining adjacent sheets of membrane roofingmaterial employs tape composed of a single layer of an uncuredelastomeric material which cures in place after application. This tapeis applied along the edge of one of the sheets to be joined and the twosheets are then overlapped. A roller is rolled along the joint to pressthe sheets into engagement with the tape. The tape, however, has alimited shelf life and may even cure before it can be used if left forprolonged periods on a hot roof or in an excessively warm storeroom.

Once the sheets of membrane roofing material have been joined to coverthe roof, the membrane must be fixed in position. The spliced membranemay be held in position by means of fastening bars which are elongatedstrips of materials such as plastic or metal. The fastening bars arepositioned in the desired location, which may overlay a lap joint, andfastened to the underlying roof structure by fasteners such as screwswhich extend through the membrane roofing material. In order to preventmoisture seepage, a layer of caulking material is applied to the bottomof the fastening bar prior to fastening it in place, and the heads ofthe fasteners are caulked after they have been inserted through thefastening bar. Some roofing manufacturers have also attempted to preventleakage by covering the fastening bar with a strip of membrane roofingmaterial applied with the contact cement and sealed with the roofingcaulk as described above with respect to the splicing of the membrane.

Emergency repairs of membrane roofing are frequently accomplished byapplication of a solution of an asphalt-type material. A permanentrepair may later be accomplished by removing the patched section of themembrane roofing material and splicing a new piece of material in itsplace.

SUMMARY OF THE INVENTION

It has been discovered that a superior roofing adhesive can beformulated by adjusting the composition thereof such that several keyproperties are controlled. These properties include the tensilestrength, elongation, modulus at 300% elongation and modulus at failureof the adhesive. The adhesion of the composition to the roofingmaterials, as measured by the peel strength and shear strength of thecomposition must likewise be controlled.

Tensile strength refers to the maximum stress (force per unit area) thata specimen of adhesive material can withstand before rupturing.Elongation measures the relative increase in length of a specimen ofmaterial at the point of rupture. The modulus at 300% elongation is theforce required to stretch a sample of the adhesive to an elongation of300% divided by the elongation of the sample expressed as a decimalrather than as a percentage. The modulus at failure is the tensilestrength divided by the elongation.

Adhesives according to the present invention are compounded to have atensile strength of at least 50 psi, an elongation of at least 600%, amodulus at 300% elongation of less than 12, and a modulus at failure ofless than 20. Preferably, however, the adhesives are compounded to havea tensile strength of at least 60 psi, an elongation of at least 800%and preferably more than 1000%, a modulus at 300% elongation of at most8, and a modulus at failure of at most 16. The adhesive composition alsopreferably has a peel strength of at least 2 pounds per inch and a sheerstrength of at least 15 psi.

Adhesives according to the present invention comprise cured butylrubbers which preferably are present only in the form of a copolymerhaving a viscosity average molecular weight greater than 100,000, incombination with appropriate tackifiers, in which the tensile strengthand other physical properties have been adjusted as discussed. Ingeneral, tensile strength and elongation may most readily be controlledby adjusting the fraction of butyl rubber in the total composition, theamount of cross-linking agent used, the amount of reinforcer used, themolecular weight and degree of mole unsaturation of the butyl rubber,and to a lesser extent the tackifiers and processing methods used. Suchadhesives may be formulated by adjusting the concentration of the butylrubber to comprise about 13-40% by weight of the total compositionexcluding the cross-linking agents, by using a butyl rubber having amole percent unsaturation between about 0.5 and 2.5 and a molecularweight of about 100,000-450,000, and by using between about 0.5-6 phr ofa quinoid cross-linking agent and at least about 2 phr of carbon black.Adhesives having tensile strengths and other physical properties in theranges set forth above may also be formulated by adjusting the butylrubber to comprise about 13-50% by weight of the total composition lessthe cross-linking agents by using a butyl rubber having a mole %unsaturation between about 0.5-2.5 and a molecular weight of about100,000-450,000, and by using between about 5-25 phr of abromomethylated phenolic resin curing agent and at least 3 phr of zincoxide.

Benzoyl peroxide is a preferred oxidizer which may be used as theactivator for the cross-linking of the butyl rubber by means of thequinone dioxime curing system. When a adhesive composition is processedat elevated temperatures, however, as may be desired to reduce itsviscosity, benzoyl peroxide causes extremely rapid cross-linking of thebutyl rubber, resulting in an almost immediate gelling of the adhesiveand making application and handling thereof more difficult. Oxidizingagents of lesser activity, such as t-butyl perbenzoate or other peroxyesters, lead dioxide and diacyl peroxides may be used to increase thecuring rate, including the gel time of the sealant composition, but thehigh temperature stability and hence the resistance to aging of sealantcompositions cured with these compounds may be reduced. In order toovercome these difficulties, two oxidizing agents capable of activatingthe cross-linking of the butyl rubber may be used. In such case, one ofthe components of the activator system should be of relatively higheractivity and the second should be of lesser activity. By adjusting therelative concentrations of the two oxidizing agents, the gel time andcuring time of the adhesive can be controlled to facilitate itsapplication. Zinc oxide and sulfur may be used in combination in theadhesive to provide superior high temperature stability and agingcharacteristics.

Although the addition of either zinc oxide or sulfur alone will providesome improvement in the high temperature stability of the adhesivecompositions, their combined use provides an increase in stability ofthe adhesive which is greater than that expected from their independentuse. Preferably, concentrations of 3% zinc oxide in conjunction withsulfur or a second sulfur constituent are used to improve the hightemperature stability of the adhesive.

The adhesive is used by preparing it as a thin tape composed of adhesivematerial. Alternately, a layer of the adhesive material may be appliedto a thin strip of roofing material or other membrane material to form acover strip. In either of these two embodiments, the adhesive layer maybe backed with a standard silicone coated release paper and rolled intoa roll for transportation or storage. The present invention thusprovides an adhesive composition which is easy to transport and store,which has a long shelf life, which is easy to use, and which may be usedto form an adhesive tape or two-ply cover strip. In use, the adhesivecomposition provides an initially strong, water resistant seal betweensheets of the membrane roofing material, is usable in a variety ofweather conditions, is stable at the elevated temperatures encounteredin roofing applications, does not become brittle at low temperatures,and remains sufficiently strong and flexible to withstand the expansionand contraction of the roof. In addition, the present adhesive does notemit solvents during use which may be detrimental to laborers.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of sheets of membrane roofing materialwhich have been spliced using the adhesive tape of the presentinvention.

FIG. 2 is a perspective view of sheets of membrane roofing materialwhich have been spliced using the adhesive tape of the present inventionand illustrates one method of using a fastening bar with the presentadhesive composition.

FIG. 3 is a perspective view of sheets of membrane roofing materialwhich have been spliced using the adhesive tape of the present inventionand illustrates another method of using a fastening bar with the presentadhesive composition.

FIG. 4 is a perspective view of a sheet of membrane roofing materialwhich has been spliced using the adhesive tape of the present inventionand illustrates one method of using the two-ply cover strip with afastening bar.

FIG. 5 is a perspective view of a sheet of membrane roofing materialwhich has been spliced using the adhesive tape of the present inventionand illustrates another method of using the two-ply cover strip with afastening bar.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The copolymer network which provides the strength and continuity of theadhesive compositions of the present invention is comprised of curedbutyl rubber. Butyl rubber is intended to include copolymers of 96-99.5wt. % isobutylene and 4-0.5 wt. % isoprene (Butyl IIR) as well as otherrubbery copolymers of a major proportion (i.e., over 50% by weight) ofan isoolefin having from 4 to 7 carbon atoms with a minor proportion byweight of an open chain conjugated diolefin having from 4 to 8 carbonatoms. The copolymer may consist of from 70 to 99.5% by weight of anisomonoolefin such as isobutylene or ethyl methyl ethylene copolymerizedwith from 0.5 to 30% by weight of an open chain conjugated diolefin suchas isoprene; butadiene -1, 3; piperylene; 2,3-dimethyl-butadiene -,3;1,2-dimethyl-butadiene -1,3 (3-methyl pentadiene -1,3); 1,3 -dimethylbutadiene -1,3; 1-ethyl butadiene -1,3 (hexadiene -1,3); 1,4-dimethylbutadiene-1, (hexadiene -2,4); the copolymerization being effected bythe usual manner of copolymerizing such monomeric materials. "Butylrubber" as used herein also includes halogenated butyl rubber, of whichchlorobutyl and bromobutyl are the best known varieties. The halogen isgenerally believed to enter the butyl rubber molecule by substitution atthe allylic position in the diolefin unit. Typical chlorobutyl rubbershave about 1.0-1.5 weight per cent chlorine. "Butyl rubber" alsoincludes those varieties of butyl rubber in which conjugated dienefunctionality has been added in the linear backbone at the diolefinunits. Such conjugated diene butyls are described in U.S. Pat. No.3,816,371.

The adhesive compositions of the present invention is preferablyformulated using any of the standard high molecular weight grades ofbutyl rubber. Such grades have viscosity average molecular weights inexcess of 100,000, and most commonly in the range 300,000-450,000. Theyare to be distinguished from the low molecular weight butyl grades,which have viscosity average molecular weights on the order of one-tenthof the high weight grades. Representative examples of high weight butylgrades are Butyl 065, Butyl 165, Butyl 268, Butyl 365, Butyl 077,Chlorobutyl 1066 and Chlorobutyl 1068, all available from the Exxon OilCompany, and BUCAR 1000 NS, BUCAR 5000 NS, BUCAR 5000 S and BUCAR 6000NS, all available from Cities Service Oil Company. While the use ofbutyl rubber having a molecular weight in excess of about 450,000 willnot detract from the qualities of the adhesive, such butyl rubber iscomparatively difficult to dissolve and combine with other constituents.Thus the preferred weight range for the high molecular weight butylrubber is from 100,000 to about 450,000. Furthermore, butyl rubberhaving molecular weights in the range of 300,000-450,000 have been foundparticularly useful for formulating adhesives having desirable tensileand elongation properties, and are especially preferred.

Cross-linking of the butyl rubber may be effected by any of thewell-known curing systems, including sulfur and sulfur containingsystems, quinoid systems, and phenolic resin systems. For halogenatedbutyl, additional useable curing agents include primary amines anddiamines, secondary diamines, zinc oxide combined with alkyl dithiolcarbamates such as tetramethyl thiuram disulfide, and 1,1-1,3 dialkylthioureas. For butyl containing conjugated diene functionality,additional useable curing agents include poly-functional dieneophiles,such as ethylene glycol dimethacrylate and trimethylol propanetrimethacrylate.

Although butyl rubber may be cured using a vulcanization process (sulfurand accelerators such as mercaptobenzotiazole), such a cure results in arubber that over time is subject to degradation caused by oxygen orultraviolet radiation. Such degradation may be partially preventedthrough the use of antioxidants, such as diphenyl - p -phenylene-diamine, phenylbeta-naphthylamine and hydroquinone, andantiozonants, such as N,N'-di (2-octyl) - p - phenylenediamine andN-(1-3-demethyl-butyl) -N'- phenyl-p-phenylenediamine. Nevertheless, thecharacteristics of the resulting adhesive may change sufficiently overtime to make quinoid and phenolic resin curing systems preferable tovulcanization, where the adhesive must be capable of lasting years in aharsh environment.

Quinoid cures depend on cross-linking through the nitroso groups ofaromatic nitroso compounds. In the quinoid curing system, p-quinonedioxime and p,p-di-benzoylquinone dioxime are preferred as the curingagents. Other suitable curing agents include dibenzoyl-p-quinonedioxime, p-dinitrosobenzene and N-methyl-N,4-dinitrosoanilene, thelatter two being available on a clay base as "Polyac" from E. I. duPontde Nemours & Co. and as "Elastopar" from Monsanto Chemical Co.,respectively. The cross-linking activators which may be employed in thesealant composition include inorganic peroxides, organic peroxides(including diaroyl peroxides, diacyl peroxides and peroxyesters) andpolysulfides. Exemplary are lead peroxide, zinc peroxide, bariumperoxide, copper peroxide, potassium peroxide, silver peroxide, sodiumperoxide, calcium peroxide; metallic peroxyborates, peroxychromates,peroxycolumbates, peroxydicarbonates, peroxydiphosphates,peroxydisulfates, peroxygermanates, peroxymolybdates, peroxynitrates,magnesium peroxide, sodium pyrophosphate peroxide, and the like; theorganic peroxides such as lauryl peroxide, benzoyl peroxide,2,4-dichlorobenzoyl peroxide, t-butyl peroxybenzoate, dibenzoylperoxide, bis (p-monomethoxy-benzoyl peroxide, bis (p-nitrobenzoyl)peroxide, and phenacetyl peroxide; the metallic polysulfides such ascalcium polysulfide, sodium polysulfide, potassium polysulfide, bariumpolysulfide and the like, some sulfur bearing organic compounds such asdisclosed in U.S. Pat. No. 2,619,481, and the organic polysulfides,which possess the general formula R--(S)_(x) --R where R is ahydrocarbon group and x is a number from 2 to 4. The actualcross-linking agent is believed to be the oxidation product of quinonedioxime, p-dinitroso benzene.

The quinoid curing agent/cross-linking activator combination which hasbeen found to result in the shortest gel time is the p-quinonedioxime/benzoyl peroxide combination. The preferred concentration ofp-quinone dioxime is 0.5-6 phr. The preferred concentration of benzoylperoxide is 1.5-18 phr. Accelerators may be employed as appropriate. Forexample, cobalt napthenate may be used in combination with t-butylperoxybenzoate, and chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) maybe used in combination with t-butyl peroxybenzoate or benzoyl peroxide.

At higher temperatures, however, the use of benzoyl peroxide as thecross-link activator causes extremely rapid gelling of the adhesive. Thegel time of the adhesive is the time required for the cross-linkingreaction between the butyl rubber and the cross-linking agent to proceedto the point that it has become extremely viscous and no longer flows ata perceptible rate.

In order to facilitate handling of the adhesive it may be desirable toadjust the gel rate by using a less active oxidizing agent, such ast-butyl perbenzoate or other peroxy esters, as a part of the curingsystem. Such oxidizers can be mixed with benzoyl peroxide in varyingamounts to adjust the gel time and to permit the mixing and handling athigher temperatures. By adjusting the concentration of these twoactivators, a relatively short get time can be obtained without anoverly rapid curing of the adhesive. This occurs because the benzoylperoxide initially causes rapid cross-linking under the elevatedtemperatures, but because of its lowered concentration does not completethe gelling and curing. The relatively less active t-butyl perbenzoatethen completes the curing over a longer time span. By adjusting therelative concentrations of the two oxidizing agents, the sealant can becompounded to get at a sufficiently rapid rate to a consistency whichprevents running and yet remain fluid long enough to permit easyhandling.

The high temperature stability of the adhesive composition and hence theresistance to aging can be greatly improved by the addition of zincoxide and sulfur thereto. Although sulfur may be used to cure butylrubber by vulcanization, it does not serve as such in the presentinvention since the adhesive is not heated during the curing process toa temperature sufficient to cause any appreciable sulfur cross-linking.

Preferably, the zinc oxide is used in an amount not less than 1% byweight of the adhesive composition. As zinc oxide is a suitable fillermaterial, it may be added in any amount greater than the 1% minimumwhich does not adversely affect the characteristics of the adhesive. Thesulfur should be added in concentrations not less than 0.5-1.0 parts per100 parts of butyl rubber. Sulfur-containing compounds may also be usedas the sulfur constituent in lieu of or in combination with the sulfur.These sulfur constituents should be used in like concentrations to thatsuitable for sulfur with adjustments made for their increased molecularweight and the number of sulfur-bearing functional groups per molecule.In addition to sulfur, suitable sulfur compounds which may be used assulfur constituents of the adhesive composition include benzothiazyldisulfide mercaptobenzothiazole and its derivatives and salts,dithiocarbamic acid and its derivatives and salts, tetraethylthiuramdisulfide, tetramethylthiuram monosulfide, zinc dibutyldithiocarbamate,tellurium diethyldithiocarbamate, dipentamethylenethiuram tetrasulfide,and thioureas. Materials which provide sulfur during the cross-linkingor aging processes may also be used. Such compounds includeaminodisulfides, such as dimorpholene disulfide, tetramethylthiuramtrisulfide and polysulfide, polymeric alkylphenol sulfides of sulfurrank equal to or greater than 3, and alkyl or aryl polysulfides ofsulfur rank equal to or greater than 3. In general, vulcanizationaccelerators and materials which provide sulfur either by themselves orthrough interaction with other materials are usable as a sulfurconstituent of the adhesive.

The use of zinc oxide, sulfur or a sulfur-bearing compound alone, asdescribed above, will result in the improvement of the high temperaturestability of the adhesive. The combined use of the zinc oxide and sulfuror a sulfur compound, however, results in improvements in the stabilitywhich is greater than that expected from the use of zinc oxide, sulfuror a sulfur compound alone. The high temperature stability can be evenfurther improved by use of a second sulfur-containing compound, such asbenzothiazyl disulfide in conjunction with sulfur.

Although discussed herein with respect to peroxide activatedcross-linking reactions, it is believed that the use of zinc oxide andsulfur will also improve the stability of adhesives prepared using thephenolic resin curing system described herein.

The phenolic resins which may be used as curing agents in this inventioninclude halomethylated alkyl phenolic resins, methylolphenolformaldehyde resins, and related species. Bromomethyl alkylphenolic resins available from Schenectady Chemicals, Inc. under thetradenames CRJ-328 and SP-1056 are suitable. The preferred concentrationof phenolic resin is 5-25 phr. Such resins do not require the use ofactivators.

The compositions of the present invention includes one or moretackifying agents which enable the composition to adhere to the tire, toa puncturing object, and to self-heal over a puncture hole after thepuncturing object has been removed. In general, any tackifying agentcompatible with a butyl rubber system may be used. Such agents includepolybutenes, polypropenes, paraffinic oils, petrolatum, phthalates, anda number of resins including polyterpenes, terpene-phenolics,blocked-phenolics, modified rosin and rosin esters, and hydrocarbonresins. Preferred tackifiers are polyisobutylenes and hydrocarbon orphenolic resins.

The kind and quantity of tackifiers used should be chosen to provideadequate adhesion and plasticity across the anticipated range oftemperatures to which the adhesive will be exposed. Of the preferredtackifiers listed with respect to the sealant composition, thepolybutene sold under the trademark H-300 by AMOCO and the phenolictackifier sold by Schenectady Chemicals, Inc. under the trademark SP1068 are especially preferred.

The adhesive compositions of the present invention may include one ormore reinforcing agents or fillers. For compositions cured by a quinoidcuring system, one of the reinforcing agents should be finely dividedcarbon. Carbon, such as carbon black, provides reaction sites for thequinoid curing process, and should comprise at least 2 parts of theadhesive by weight for each 100 parts of butyl rubber. Preferredconcentrations of carbon black are 6 phr or greater. The substancecomprising the remainder of the reinforcing agent may either be carbonblack or some other suitable substance selected on the basis of thedesired color of the adhesive. For compositions cured by a phenolicresin curing agent, one of the reinforcing agents must be at least 3 phrof zinc oxide. The preferred concentration of zinc oxide is 5-30 phr.Carbon black may also be used with compositions cured by means ofphenolic resins, but its presence is not required. Other well-knownreinforcing agents and fillers for butyl rubbers include aluminumhydrate, lithopone, whiting, clays, hydrated silicas, calcium silicates,silicoaluminates, magnesium oxide, and magnesium carbonate.

The adhesive composition also includes one or more fillers as describedwith respect to the sealant composition. If carbon black or zinc oxideis used in connection with a quinoid or phenolic resin curing system, orfor improving high temperature stability, such carbon black or zincoxide also serves as a part of the filler material.

To aid in maintaining sufficient tackiness and thermal stability atelevated temperatures, the adhesive compositions of the presentinvention may include a thermoplastic and elastomericpartially-hydrogenated block copolymer up to about 10 wt. % of thecomposition, the block copolymer having a general configuration ofA--(B--A)₁₋₅ wherein prior to hydrogenation each A is a monovinyl arenepolymer block and each B is a conjugated diene polymer block. Typical Amonomers are styrene, alpha methyl styrene and ring alkylated styrenes.Typical B monomers are butadiene and isoprene. The A blocks make up theend groups and typically comprise about one third of the copolymer byweight, and the B blocks make up the mid groups and the balance of thecopolymer. The copolymer is partially hydrogenated so that theconjugated diene block segments are substantially fully saturated. Themonovinyl arene polymer block segments are not appreciably saturated.Hydrogenation in this fashion enhances the utility of the blockcopolymer as an oxidation and high temperature-degradation resistantconstituent of the adhesive composition. The average molecular weight ofthe copolymer is in the range of about 60,000 to 400,000. Blockcopolymers of this type are described in U.S. Pat. No. 3,595,942.

Adhesive compositions according to the present invention are compoundedby selecting with the exception the components and adjusting theirconcentrations such that the adhesive has a tensile strength of at least50 psi, an elongation of at least 600%, a modulus at 300% elongation ofless than 12, and a modulus at failure of less than 20. Preferably,however, the adhesive is compounded to have a tensile strength of atleast 60 psi, an elongation of at least 800% and preferably more than1000%, a modulus at 300% elongation of at most 8, and a modulus atfailure of at most 16.

If the tensile strength of the adhesive is insufficient, it may besubject to tearing or shearing and may thus fail in use. The limit onthe elongation of the adhesive relates to the ability of the adhesive toconform to irregular surfaces, as may be encountered when the adhesiveis applied over a lap joint or fastening bar. If the sealant has aninadequate elongation, it may pull away from the irregular surface,resulting in leaking of the roof. The modulus at 300% elongation is afunction of the force necessary to stretch the adhesive to an elongationof 300%. As such, if the modulus is too high, very small deflections ofthe membrane roofing material may generate excessive forces in theadhesive. Adhesives with a high modulus at 300% elongation further maybe unable to maintain adhesion over irregular surfaces.

Tensile strength and elongation of the adhesive may be adjusted asdescribed in connection with the examples herein. Generally, changeswhich affect the tensile strength and elongation also affect the modulusat 300% elongation and the modulus at failure. For example, the tensilestrength of the sealant and adhesive described herein may be increasedby increasing the cross-link density. A large increase in the cross-linkdensity, however, will increase both the modulus at 300% elongation andthe modulus at failure. Changes to the kind and quantity of tackifiersalso affect the tensile strength, elongation, modulus at 300%elongation, and modulus at failure as is demonstrated by the examplesherein.

In addition to the required tensile strength, elongation, modulus at300% elongation, and modulus at failure, the adhesive should also becompounded to have a shear strength of greater than 15 psi and a peelstrength greater than two pounds per inch at 70° F. The shear strengthand peel strength relate to the ability of the adhesive to adhere to anobject such as membrane roofing material and are related to the amountsand kinds of tackifiers used.

Tensile strength is the stress per unit area that a sample of adhesivecan withstand before rupturing. As used herein, tensile strength isdetermined by first curing a sample of the adhesive in a thin sheet.Dumbell shaped specimens of the adhesive are then cut using ASTM die"D", and the dimensions of the dumbell shaped specimen are determined.The speciment is then placed in a conventional Dillon tensile testingapparatus having jaws which grip it at its wider end portions, and thespecimen is stretched at a cross-head speed of 10 inches per minuteuntil rupture. The tensile strength is the force at rupture divided bythe initial cross sectional area of the narrow portion of the specimen.

Elongation, as used herein, is determined by a procedure identical tothat for tensile strength. The elongation, expressed as a percentage, iscalculated by subtracting the initial length of the specimen from itslength at rupture, multiplying by 100, dividing by the initial length,and then if necessary by multiplying the result by a correction factorwhich compensates for any material which may have been pulled out of thejaws gripping each end of the specimen. The initial and final rupturelengths are determined by measuring the distances between the jaws. Thusthe specimen being elongated includes not only the narrow, centralportion but also some of the wider end portions of the specimen.

The modulus of the adhesive composition at various elongations is alsodetermined by a procedure similar to that for determining tensilestrength. The modulus is equal to the force required to stretch thesample to a predetermined elongation divided by the elongation expressedas a decimal ratio rather than as a percentage. The modulus at failureis thus the tensile strength divided by the final elongation.

The shear strength of the adhesive is determined by a procedure similarto that for testing tensile strength. Two 1-inch by 2-inch pieces ofmembrane roofing material are prepared and are cleaned and/or primed ifdesired. A 1-inch by 1-inch piece of sealant is then applied to one endof a first piece of the membrane roofing material, and the second pieceof membrane roofing material is aligned axially with the first piece andapplied to overlap only that portion of the first piece which is coveredby sealant. A lap joint is thus formed with the one square inch ofsealant disposed between the two pieces of membrane roofing material.Uncoated ends of the membrane roofing material extend in oppositedirections from the lap joint.

In order to ensure that the adhesive is bonded to the strips, a handroller is then passed over the lap joint ten times. The free ends of thestrips are gripped in the jaws of a tensile strength testing apparatusand pulled apart at the rate of two inches per minute. The force appliedto the test sample during the spreading process is monitored and theforce at rupture of the sample is the shear strength.

The peel strength is determined by a similar procedure. Two 1-inch by3-inch pieces of EPDM or other membrane roofing material are prepared,and a 1-inch by 2-inch sample of the adhesive is applied to one end ofthe first strip. The second strip is then positioned directly above thefirst strip and a hand roller is passed over the sample ten times, usinghand pressure, to ensure that the strips and adhesive are completelybonded. The free ends of the strips of membrane material, which extendfrom the same end of the sample are gripped in the jaws of the tensilestrength testing apparatus and pulled apart at the rate of two inchesper minute. The force applied to the sample is monitored until thesample has been completely peeled apart. The peel strenght is theaverage force applied to the sample during the peeling process.

The above described tests may readily be carried out by those skilled inthe art, and the results of such tests may be used to guide theformulation of the adhesive composition of the present invention.

Adhesives having tensile strength, elongation, modulus at 300%elongation, modulus at failure, and shear and peel strength swell ratioswithin the ranges set forth above may be formulated by including in thecompositions of the present invention 13-40% by weight of butyl rubberhaving a mole % unsaturation of between about 0.5 and 2.5, and byemploying at least 2 phr of carbon black and about 0.5-6 phr of aquinoid cross linking agent. The remainder of such compositions arecomprised of appropriate tackifying agents, block copolymers, fillers,pigments, and the like. Sealant compositions having physical propertiesas described above may also be formulated by employing 13-50% by weightof butyl rubber having a molecular weight greater than about 100,000 anda mole % unsaturation of between about 0.5 and 2.5, 5-25 phr of aphenolic resin curing agent, at least 3 phr of zinc oxide, with theremainder of the composition comprising tackifying agents and othermodifiers.

Because the adhesive compositions described herein have the uniqueability to resist oxidation and to remain stable and effective over awide temperature range, and adhere to irregular surfaces they havenumerous applications in the roofing industry as well as in otherapplications in addition to their utility as roofing adhesives. Sincethe environments to which a roofing adhesive is subjected is the mostsevere, the following examples relate the sealant composition to thisenvironment for purposes of illustration. It will be understood that theratio of the essential ingredients may be varied within the ranges setforth above and that other compounding materials may be replaced byand/or supplemented with such other materials as may be appropriate todeal with the environment contemplated.

Preferably, the adhesive composition is formed either as a single plytape of about 0.03-0.05 inch thickness or as a two ply tape or coverstrip comprising a layer of the adhesive composition backed by a sheetof EPDM roofing material or other membrane material. Such membranematerial may be single calendered, of course, since the adhesive layerwill seal any pinholes or other minor defects therein. In either ofthese configurations, the adhesive layer may be backed with a standardsilicone coated release paper and rolled into a roll for transportationor storage.

The adhesive composition of the present invention may be used in avariety of ways in connection with membrane roofing material. FIG. 1illustrates a lap joint formed between two parallel sheets of suchmaterial 1, 2. To form this lap joint, the sheets of membrane roofingmaterial are laid out parallel to one another with their adjacent edgesoverlapping approximately two to four inches. The upper sheet 2 is thenfolded back so that it no longer overlaps the first sheet and theoverlapping edges are cleaned and primed if desired. Solvents such ashexane, toluene or white gasoline may be used for cleaning the sheets ofmembrane roofing material 1, 2. Generally, the sheets of membraneroofing material are approximately 0.04-0.06 inches in thickness. A tapecomprising a single layer of the adhesive material, which is preferablyabout 0.03 to 0.05 inches in thickness, is then applied along the edgeof one of the sheets 1, 2. If the adhesive tape has been supplied inroll form with the adhesive composition backed by a release paper, theadhesive material 3 may be rolled onto the edge of one of the sheets 1,2 as the backing paper is removed. The upper sheet 2 is then folded backinto overlapping relation with the lower sheet 1 and a roller passedalong the lap joint to ensure a good bond between the two sheets 1, 2and the adhesive 3. Alternately, the tape could be applied, for example,to the lower sheet 1 with the backing paper adhered to its uppersurface. The upper sheet 2 can then be folded back into overlappingrelation and the two sheets 1, 2 and adhesive 3 pressed into engagementwith a roller as the backing paper is peeled from the upper surface ofthe adhesive tape 3.

FIG. 2 illustrates another method of use of the adhesive tape of thepresent invention. As described above, once membrane roofing materialhas been spliced, fastening bars are used to maintain the spliced sheetof membrane roofing material in position on the roof. According to thismethod, a lap joint is formed between two adjacent sheets of membraneroofing material 4, 6. A layer of adhesive tape 7 is used to join thesesheets 4, 6 to one another as described in connection with FIG. 3. Afastening bar 8 is then positioned along the lapped joint so that itoverlies the layer of adhesive material 7. Fasteners such as nails orscrews are then extended through the fastening bar 8 and overlappingsheets 4, 6 into the underlying roof structure. The layer of adhesivetape 7 serves not only to bond the two sheets of roofing material 4, 6together, but also to seal the holes made by the fasteners.

FIGS. 3 and 4 depict two additional methods of fastening joined sheetsof membrane roofing material to the underlying roof structure. Accordingto this method, a lap joint is formed between overlapping sheets ofmembrane roofing material 9, 11 by a layer of adhesive tape 12 asdescribed in connection with FIG. 1. A fastening bar 13 is thenpositioned along the lap joint with a layer of adhesive material 14disposed between it and the upper surface of the overlapping sheet ofmembrane roofing material 11. Fasteners driven through the fastening barinto the underlying roof structure must thus pass through two layers ofthe adhesive material 12, 14 further reducing the likelihood of moisturepenetrating through the holes made by the fasteners.

The method illustrated in FIG. 4 provides an even greater barrier topenetration of moisture. As in the embodiment of FIG. 2, a fastening bar16 is positioned atop a lap joint formed by two sheets 17, 18 ofmembrane roofing material and a layer of adhesive tape 19. Fasteners areextended through the fastening bar 16, the two sheets 17, 18 and theadhesive tape 19 and into the underlying roof structure. A cover strip21, comprising a layer of the adhesive composition 22 applied to a stripof the membrane roofing material 23 is then used to cover the fasteningbar and the joint between the two sheets of membrane roofing material17, 18. The method illustrated by FIG. 5 is identical to that of FIG. 4,with the exception that a layer of adhesive tape 24 is interposedbetween the fastening bar 13 and the upper sheets of membrane roofingmaterial 12.

It will be apparent to those skilled in the art that the adhesivecomposition and cover strip described above may be used equally forapplying new roofing and for repairing existing roof structures.

The adhesive compositions of the following examples were prepared bycombining the ingredients listed in Table IV in the proportionsindicated, all proportions being given by dry weight unless otherwiseindicated.

                  TABLE I                                                         ______________________________________                                                 A     B     C       D   E     F   G                                  ______________________________________                                        Butyl      35      35    35    35  35    35  35                               Rubber.sup.1                                                                  Piccotac.sup.2                                                                           5       5     --    --  --    --  --                               H-300.sup.3                                                                              49      44    54    49  46    54  54                               SP 1068.sup.4                                                                            --      --    --    5   5     --  --                               Dioctyl    --      5     --    --  3     --  --                               Azelate                                                                       Carbon Black                                                                             2       2     2     2   2     2   2                                ZnO        9       9     9     9   9     9   9                                S (phr)    1       1     1     1   1     1   1                                Mercaptobenzo-                                                                           --      2     --    3   5     --  5                                thiazole (phr)                                                                Para-Quinone                                                                             2       2     2     2   2     2   1                                Dioxime (phr)                                                                 Benzoyl    --      --    --    6   6     3   1.5                              Peroxide (phr)                                                                T-Butyl    12      12    12    --  --    --  --                               Perbenzoate (phr)                                                             ______________________________________                                         .sup.1 The butyl rubber used was a mixture composed of 69% Butyl 165 and      31% Butyl 365.                                                                .sup.2 A hydrocarbon resin having a softening point of 97° C. is       available from Hercules, Incorporated under the trademark "Piccotac B".       .sup.3 A polybutene having an average molecular weight of 1290 available      from AMOCO under the trademark "H300"                                         .sup.4 SP 1068 is a phenolic thermoplastic tackifier sold by Schenectady      Chemicals, Inc.                                                          

EXAMPLES I-III

Samples of the adhesive composition were prepared according to FormulasA, B and C of Table I. Adhesive tape of 0.05 inch thickness was preparedfrom each of these samples and cured at ambient temperature for one dayand at 158° F. The samples were then tested at ambient temperature fortensile strength, elongation, modulus at 300% elongation, modulus atfailure, and shear and peel strength. EPDM sheeting was used in testingthe peel and shear strengths of the samples. Since the EPDM materialused in the testing of samples I-III was relatively clean, hexanecleaning was deemed unnecessary. All other samples, however, wereapplied to EPDM sheeting which had been cleaned with hexane. The shearand peel tests were also performed using EPDM membrane which had beentreated with primer. The results of these tests are set forth in TableII. The tensile and shear strengths are given in psi, the elongation inpercent and the peel strength in pounds per inch. The peel strength ofthe samples is given in pounds per inch and the shear strength in poundsper square inch.

                  TABLE II                                                        ______________________________________                                                        Unprimed Primed                                               Example                                                                              T     E      M.sub.300                                                                          M.sub.f                                                                            Peel Shear Peel Shear                           ______________________________________                                        1      62    1719   2.05 3.58 5.0  15.4  9.5  39                              2      56    1396   2.13 4.00 3.1  14.4  9.0  38.5                            3      67    1312   2.54 5.08 3.4  14.5  9.0  41                              ______________________________________                                    

The samples of these examples had lower than normal values for shear andpeel strength. As mentioned above, however, the EPDM membrane used fortesting the peel and shear strengths, was not cleaned prior toapplication of the adhesive composition and thus the lower values areexpected. The testing of these three samples also demonstrates thebenefits of priming the EPDM roofing material. The primer, distributedby Hughson Chemicals, Lord Corporation, under the trademark TS 3320-19was diluted to 20% strength by weight with hexane prior to use. Theresultant increases in both the shear and peel strengths of the adhesivewere quite significant.

It should be noted from these examples that adjustments made to thekinds and quantities of tackifiers and plasticizers used in the sealantresulted in changes in the physical properties of the sealant. Forexample, the formulations A and C differ only in that formulation Ccontains an additional five parts of polybutene in lieu of the fiveparts of Piccotac used in formulation A. As a result, the tensilestrength of the sample of Example III was greater than that of ExampleI, and elongation of the sample of Example III was less than that ofsample I. Of course, such an increase in the tensile strength anddecrease in elongation resulted in an increase in both the modulus at300% elongation and the modulus at failure.

EXAMPLE IV

A sample was prepared according to formulation D of Table I in a layerof 0.05 inch thickness and cured at 158° F. for one day. This examplediffers from the previous examples in its use of the tackifier SP 1068and in its use of benzoyl peroxide as the curing agent. This sample hada tensile strength of 99, an elongation of 1333, a modulus at 300%elongation of 5.74, and a modulus at failure of 7.40. The peel strengthof the sample was 7.5 pounds per inch, and the shear strength 33.5pounds per square inch at ambient temperature when applied to hexanecleaned but unprimed membrane. This formulation thus satisfies thecriteria for an acceptable adhesive composition.

EXAMPLE V

A sample of the adhesive composition was compounded according toformulation E of Table I and prepared and cured in like manner to theadhesive tape of Example IV. The formulation of the tape of this examplediffers from that of the preceding example in that a small amount of thepolybutene tackifier has been replaced by an equal amount of dioctylazelate. In addition, the amount of mercaptobenzothiazole has beenincreased. The tensile strength of this sample was 82 psi, theelongation was 1180%, the modulus at 300% elongation was 7.40, and themodulus at failure was 7.06. The peel strength of the adhesive tape was7 psi, and the shear strength 30.5 psi when applied to hexane cleanedbut unprimed membrane. As with Examples I and III, the replacement ofpolyisobutylene with dioctyl azelate has been accompanied by decreasesin the tensile strength and elongation, as well as in peel and shearstrength. The physical properties are within the preferred rangeshowever and as such the adhesive of this example would functionacceptably.

EXAMPLE VI

An adhesive tape was prepared in accordance with the preceding twoexamples using formulation F of Table I. This formulation does notinclude the SP 1068 tackifier, but rather uses an increased amount ofpolybutene tackifier. The tensile strength of the sample was 139 psi,the elongation 973%, the modulus at 300% elongation was 5.60, and themodulus at failure 14.3. The peel strength of the adhesive was 4 poundsper inch, and the shear strength 25 pounds per inch when applied tohexane cleaned but unprimed membrane. Again, an acceptable adhesivecomposition may be prepared as per this example, even though theelongation is below the most preferred value.

EXAMPLE VII

An adhesive tape was prepared as in the preceding three examples usingformulation G of Table I. This adhesive composition differs from that ofExample VI in that it includes only half the cross-linking agent andcross-link activator. As a result, this sample is not as highlycross-linked as the sample of Example VI. Accordingly, the tensilestrength is only 61 psi, and the elongation has increased to 1515%. Themodulus at 300% elongation is 2.02, and the modulus at failure is 3.99.The peel strength of the sample was 5.3 pounds per inch, and the shearstrength 16.18 psi when applied to hexane cleaned but unprimed membrane.The composition of this example is this usable as a suitable roofingadhesive.

I claim:
 1. A monolayer membrane roofing material with joint laminatewhich comprises two monolayer sheets of non-tacky, non-adhesive, fullycured elastomeric roofing membrane material, overlapped along arelatively small section of their total width, a tapelike adhesive layeradapted to be disposed only between the overlapped sections of thesheets, adhesive layer comprising a permanently tacky cured butyl rubberbased composition comprising the reaction product of butyl rubber, acrosslinking system for said butyl rubber, a tackifier compatible withbutyl rubber and a filler material, the concentrations of saidconstituents being chosen such that said composition has a tensilestrength of at least 50 psi, an elongation of at least 600%, a modulusat 300% elongation of not more than 12, a modulus at failure of not morethan 20, the laminate exhibiting a shear strength of at least 15 psi anda peel strength of at least 2 pounds per linear inch.
 2. The laminate ofclaim 1 wherein said composition comprises zinc oxide and a sulfurconstituent whereby the resistance of the layer to heat aging isimproved.
 3. The laminate of claim 1 wherein the butyl rubber portion ofsaid composition comprises 13-50% by weight of said compositionexclusive of the cross-linking system and any sulphur constituent. 4.The laminate of claim 3 wherein the cross-linking system for saidcomposition comprises a quinoid cross-linking agent and an activator forsaid cross-linking agent.
 5. The adhesive tape of claim 4 wherein thecross-linking agent is p-quinone dioxime present in an amount less thanabout six parts by weight per hundred parts butyl rubber.
 6. Theadhesive tape of claim 5 wherein the butyl rubber portion of saidcomposition comprises 13-40% by weight of said composition exclusive ofthe cross-linking system and any sulfur constituent.
 7. The adhesivetape of claim 3 wherein the cross-linking system for said compositionincludes 5-25 parts of a phenolic cross-linking agent per hundred partsbutyl rubber.
 8. The adhesive tape of claim 1 wherein said layer furthercomprises flexible membrane layer adhered to one side of saidcomposition layer.
 9. The laminate of claim 1 wherein the concentrationof the constituents of said composition is chosen such that saidcomposition has tensile strength of at least 60 psi, an elongation of atleast 800%, a modulus at 300% elongation of not more than 8 and amodulus at failure of not more than
 16. 10. The laminate of claim 2wherein said sulfur constituent comprises sulfur andmercaptobenzothiazole.
 11. The laminate of claim 2 wherein the sulfurconstituent is present in an amount equivalent to at least 0.5 partssulfur per hundred parts butyl rubber; and wherein said composition iscompounded such that substantially all cross-linking of the butyl rubberis accomplished by said cross-linking system.